Pneumatic conveying systems are used to transport large quantities of particulate material through pipes. Examples of particulate material include powders, granules, pellets, seeds, beans, nuts, pasta, pet foods, snack foods, and other similar items. In a common pneumatic conveying system, a fluid, usually air, is blown through the pipes. The air enters the pipes through a filtered air inlet. The particulate material enters the pipes through a material inlet. The air is mixed with the particulate material and together, the air and particulate material moves through the pipes. Both the air and the particulate material exit the pipes through an outlet.
Dilute phase conveying occurs when the particulate material is transported at a relatively high velocity (i.e., above the saltation point). Particles are suspended in the air stream generated by a low pressure blower to move at approximately the same velocity as the air stream. This results in a relatively low product to air ratio (i.e., less than 15:1). This also results in high particle-to-particle and particle-to-pipe interaction. Dilute phase conveying is particularly useful for conveying dry materials such as flour, in which particle shear and breakdown from high particle-to-particle and particle-to-pipe interaction is less common and/or less objectionable.
Dense phase conveying occurs when the particulate material is transported at a relatively low velocity (i.e., well below the saltation point). A positive displacement blower is located upstream from the particulate material inlet. The positive displacement blower increases fluid (air) pressure within the pipes downstream of the positive displacement blower. Because the particles are not suspended in the fluid (air), they drop to the bottom of the pipe. The pressure from the positive displacement blower pushes the particles together into lumps or “slugs” within the pipe. The slugs of material are transported through the pipe with a pocket of fluid (air) between each slug. Dense phase conveying usually achieves a higher product to air ratio than dilute phase conveying. The lower velocities also result in lower particle-to-particle and particle-to-pipe interaction.
Regardless of whether dilute phase or dense phase conveying is utilized, it is often desirable and/or necessary to clean and sanitize the interior of the pipes through which product is conveyed. For example, when the material being conveyed is a food product (whether for human or pet consumption) that is highly susceptible to contamination by bacteria or other contaminants, it is often necessary to sanitize the interior of the pipes. In some cases contaminated product will unknowingly be conveyed through a system (such a pet food contaminated with salmonella), and when such contamination is discovered, the entire system must be brought offline and sanitized before it can be used for conveying any other materials. Because of the size and nature of these conveying systems, they generally are designed as clean-in-place (CIP) systems, meaning that the conveying lines (pipes) are cleaned and/or sanitized on site and any cleaning/sanitizing equipment is permanently located at and/or transported to the location of the conveying lines.
A number of systems and methods currently exist for cleaning conveying lines, such as the use of line pigs, dry ice or a material flush. For one example, in dilute phase conveying systems in particular, pipeline “pigs” are often utilized to clean deposits from the interior walls of the conveying lines. Pigging is accomplished by inserting the pig (in some cases into a “pig launcher” or “launching station”—e.g. a funnel shaped Y section in the pipeline), closing/sealing the launching station, and activating the blower to cause the pig to flow through the pipeline until it reaches the receiving bin/station (or “pig catcher”) at the end of the conveying lines. The pig is then manually removed from the receiving bin by an operator that accesses the interior of the bin. A conventional cleaning “pig” comprises a generally short length of material (typically shaped as a ball or cylinder) that spans the inner diameter of the pipe it is designed to clean, such that the exterior of the pig engages the interior walls of the pipe to remove material deposits from those walls as it travels through the conveying lines. Typically, a pig's diameter is at least as large as, and often larger than the diameter of the pipe it is going to clean so that the exterior of the pig is in continuous contact with the inner walls of the pipe. Various pig designs include exterior brushes, fluid ejecting nozzles, and other features to aid in cleaning the walls of the pipe.
Once the lines are cleaned, several conventional systems have been utilized for sanitizing the cleaned lines. One option is a full wet CIP loop, in which a large amount of sanitizing solution is pumped through the conveying lines, which are generally operated as a closed-loop system. Full wet CIP systems require usage of a very high volume of cleaning fluid, as well as complicated, specially designed pumps, fluid tanks, return piping (e.g. to create the loop), etc. to sanitize conveying lines. Proper disposal of the used sanitizing fluid is often an issue, particularly as environmental regulations increase. In addition, due to the large amount of wet residue remaining of the sanitizing fluid, the conveying lines must remain offline for extended periods of time until they are allowed to dry out. As such, full wet CIP systems are often not practical for use in sanitizing conveying lines in which primarily dry product is transported.
Another option for sanitizing already cleaned conveying lines utilizes sanitizing pigs that are similar to those utilized for cleaning conveying lines. These sanitizing pigs are typically constructed of a porous material such as a foam/sponge material that is capable of soaking up the sanitizing solution. The pigs are “loaded” with sanitizing solution and then conveyed through the pipes in the same manner discussed above with respect to cleaning pigs. The sanitizing solution is then spread onto the inner walls of the pipes through direct contact with the exterior surfaces of the pigs. Such methods result in uneven application of sanitizing solution, as more solution will be applied early on when the pig is more heavily soaked, and decrease as the pig travels through the pipes. In addition, due to the materials used to make sanitizing pigs capable of soaking up fluid, such pigs are not compatible with a number of sanitizing solutions, which would destroy the pig material. Moreover, it is necessary for an operator to access the interior of the receiving bin to remove the pigs after they are conveyed through the pipes.
Another option for sanitizing already cleaned conveying lines utilizes a high pressure wet “snake” that includes a special spray nozzle attached to the end of a supply line. In such systems, a large volume of fluid is pumped out the nozzle to propel the snake and supply line through the pipe. Thus, such systems leave a large amount of wet residue behind, creating the same or similar disposal and drying time difficulties discussed above with respect to full wet system.
Other options for sanitizing already cleaned conveying lines often utilize line pigs attached to a tether to pull a spray rig through the conveying lines. The pig is conveyed through the pipes and retrieved at the receiving bin by an operator. The spray rig is then pulled through the lines using the tether. The spray rig is then pulled back out of the conveying lines, spraying sanitizer as it is retracted. One exemplary system is the BioMist system, which utilizes an alcohol based sanitizing solution, and requires compressed carbon dioxide for atomization of the solution. The alcohol based sanitizing solution of the BioMist system is often undesirable due to the potential for vapor build up in enclosed system to potentially explosive levels. Moreover, these type of systems are very time consuming, require operators to access both the launch side and receiving side of the system, and expose operators to the interior of the system to retrieve the pig and tether lines.
Other systems utilize spray rigs that are incorporated into or attached to a pig device and propelled through the conveying lines with the pig by the blower for the pipeline. Refraction of the spray rigs is often difficult because the pig tends to get stuck in the pipeline. Thus, such systems often require removal of the pig from the spray rig prior to retraction of the rig from the pipeline. This requires the operator to access the interior of the conveying system as the receiving bin. Moreover, in many dilute phase conveying systems, the high velocity of travel of the pig through the pipes can result in damage to the spray nozzle.
Therefore, it would be beneficial to provide a system and method for sanitizing pneumatic conveying lines that overcome the deficiencies of the prior art discussed above.